The invention concerns a method and an apparatus for testing and measuring blood clotting time, in which blood or blood plasma and a reagent are introduced into a measuring cuvette and the clotting time is measured electro-optically with the aid of a stirring element which is arranged in the measuring cuvette, can be attracted magnetically and is driven by a magnetic stirring device arranged outside the measuring cuvette.
Methods and apparatuses of this type (DE-PS 3,127,560, EP-PS 0,090,192) permit very multifarious and dissimilar types of blood clotting time measurement. Although very accurate values are obtained, the costs of operation by trained personnel are necessarily high.
Although automatic methods for measuring blood clotting time are known, they cannot, however, be used for the measuring method with stirring elements mentioned at the beginning. Moreover, these methods have grave disadvantages. These disadvantages are connected with the fact that, on the one hand, the blood plasma and the reagents must be cooled before the measurement, whereas, on the other hand, the measurement must take place at a temperature which may have only very small deviations from 37.degree. C. If the reagents are not kept at a temperature of 15.degree. C., they partially decompose even after half an hour. On the other hand, if the temperature departs during measurement by only 1.degree. from 37.degree. C., there is already a measurement error of 10%.
In an automatic method for testing and measuring blood clotting time (brochure MLA Electra 800 from AHS/Deutschland GmbH), the measuring cuvettes, which have previously been filled with blood plasma by hand, are inserted into a carousel in which their temperature is controlled. When the cuvette is located at the appropriate station, the reagent is then filled into it by a pump from the cooled storage vessel through a plate-shaped element in which heating to 37.degree. C. takes place. The plasma, which has been heated to 37.degree. C., and the likewise heated reagent then meet here. The disadvantage consists, for one thing, in that the plasma still has to be filled into the measuring cuvettes by hand, and in that these measuring cuvettes then need to be inserted by hand into the carousel. A further disadvantage consists in that the plate-shaped heat exchangers take up a relatively high amount of reagent. When measurement is interrupted, it is then necessary for the reagent to be pumped back from these plate-shaped heat exchangers, since otherwise it decomposes. However, residual amounts subsequently dry on the walls, so that when restarting there is the danger of blockages or erroneous measurements. Consequently, the heat exchanger plates must be frequently replaced. Further, there is the danger of losses of relatively expensive reagent liquid. Moreover, a separate pump and a separate heat exchange surface are required for each reagent, so that with the named apparatus it is possible simultaneously to use only two reagents for one measurement. This number of reagents cannot be increased ad lib without excessive expenditure.
In a further method (brochure COAC-A-Mater-X2 from the firm Labordiagnostica Godecke) the plate-shaped heat exchangers are dispensed with. Instead of these, the hoses for the reagents are lead through a plate-shaped element, which is at a temperature of 37.degree. C. Here, after measurement has been interrupted the hoses can and/or must be cleaned or replaced, and this is likewise troublesome and expensive; there is also a high risk of erroneous measurements.
In a further previously known method (brochure ACL Automated Coagulation Laboratory from Instrumentation Laboratory), the plasma is automatically introduced into a cuvettes from a centrifuge tube. The reagents are also filled into the measuring cuvette automatically from cooled storage vessels In this process, the transfer device can also be fed intermittently to a washing device. Subsequently, the space with the measuring cuvettes arranged on a centrifuge is closed off. The measuring cuvettes are then heated, and upon reaching a temperature of 37.degree. C. are set into rapid rotation resulting in thorough mixing due to the centrifuge effect. This system likewise has various disadvantages.
For one thing, not all types of measurements are possible in the centrifuge. It is not possible to use any reagents which sediment, e.g. PTT reagent with kaolin. Again, the advantageous measurements with stirring elements are not possible. Moreover, the cuvettes must be absolutely leakproof, since otherwise at the high centrifuging rate of 1200 rpm liquid penetrates into the rotor space and contaminates it, and especially also contaminates the measuring devices. Finally, the measuring cuvettes cannot be removed automatically after the measurement, but must be taken out by hand.
The object of the invention consists in creating a method of the type mentioned at the beginning in which it is possible, by exploiting the advantages of the method with a stirring element, to conduct very many different tests with various reagents, changing rapidly from one reagent to another, the method being designed especially for automatic applications.
The object is achieved according to the invention in that blood plasma and reagent are introduced beside one another onto an essentially horizontal internal surface of a measuring cuvette provided with an opening above this surface, in that the measuring cuvette and its contents are heated to the reaction temperature, in that the measuring cuvette is pivoted in the measuring station by essentially 90.degree. in such a way that the internal surface stands essentially perpendicular and plasma and reagent flow together, and in that the measurement is subsequently carried out.